Claim CB365:

A treatment for certain back conditions, Williams flexion exercises,
recommended decreasing lordosis as much as possible. It was based on
evolutionary theory, specifically that humans evolved from quadrupeds and
that back problems are a result of our new upright posture. This
treatment protocol often impeded healing and caused great pain. Robin
McKenzie's exercises, which recommended restoring normal lordosis
(anterior convexity of the spine), are much more effective.

Source:

Response:

Williams' treatment for back pain was not based on evolutionary
theory. It was based on observations of normal people and people with
back pain. Part of his rationale was that people from African and
Asian cultures who sat on the floor had less back pain than Westerners
with their chairs.

Furthermore, Williams did not recommend decreasing lordosis all the
time, but only in cases of posterior disc bulging. It was already well
known that anything which interfered with the spine's normal curvature,
increasing or decreasing it, tended to cause pain. As even Bergman
acknowledges, the Williams flexion exercises are beneficial in cases of
spinal stenosis.

Mackenzie's exercises were more effective because they were simple and
required no special equipment, so patient compliance was much greater.